Definite possibility, although ironically shortly after the Phantoms were returned 76 Sqn was disbanded to save money and, as I understand it, to stretch out the Mirage IIIs service life through providing a larger pool of airframes to balance out the remaining life of the fleet.
Possible scenarios I have thought of include the Phantoms re-equip one of the Mirage squadrons (3 Sqn for symmetries sake), or F-4E Phantoms replace Canberras in 2 Sqn while still in Vietnam completely separate to the pre-F-111 lease, maybe 4 Sqn is reformed to take the Phantoms made surplus after the F-111s are delivered. It could be that the Phantoms are retained / acquired as a deliberate strategy to put off procuring a Mirage replacement.
Another possibility I thought of was DOA was all about the air sea gap, sea and air power, now assuming one or more of the above options has occurred and the Phantom is already in service, additional Phantoms could have been acquired to police the air sea gap and replace the RAN FAAs Skyhawks as the RAAF was now committed to providing fleet air defence. Maybe there could even be justification for a squadron of RF-4C/E to be stationed in Victoria to monitor Tasmanian dam construction.